Mechanical time fuse



Feb. 13, 1945. w. L. MCGRATH ETAL- 239,310

MECHANICAL TIME FUSE Filed Dec. 29, 1958 4 Sheets-Sheet 1 h I wwwww w\fl III R w 9 WW II M 4 w w m m T Z 5 i mW 7 INVENTOR. Wu

BY L.

Feb. 13, 1945. L. MCGRATH AL 2,369,310

' MECHANICAL TIME FUSE Filed Dec. 29,1938 4 Sheets-Sheet 2 INVENTOR.M/CMes/s MxlUa/n/ c6. mcgmt/v -W ATTORNEY.

Feb 1945- w. 1.. MCGRATH ET AL MECHANICAL TIME FUSE Filed Dec. 29, 19384 Sheets-Sheet 3 INVENTOR. MLLLLQnQ/II. fTLc aZ/Q/ BYmceJQ/LU/u IATTORNEY.

w. 1.. MCGRATH ETAL FUSE Patented Feb. 13, 1945 MECHANICAL TIME FUSEWilliam L. McGrath and Maurice P. Whitney, Elmira, N. Y., assignors toBendix Aviation Corporation, South Bend, Ind-., a corporation ofDelaware Application December 29, 1938', SerialNo. 248,224 2 Claims.(01. 10.2 s4) The present invention relates to a mechanical time fusefor explosive projectiles and more particularly to a device operated byenergy derived from the. acceleration of the projectile, for timing andactuating the firing mechanism of the projectile.

Mechanical fuses have heretofore been constructed using various types ofinertia and/or spring-actuated driving mechanism with gearing andescapement devices to control the release of the firing pin. It has beenfound possible to construct such fuse mechanism having a time scope ofthirty seconds or more with an accuracy tolerance of a few hundredths ofa second, which will operate quite consistently under laboratory test.conditions. Under conditions of actual use, however, it has been foundthat in spite of accurate workmanship and close fitting, discrepanciesin operation occur, and it is even possible for the devices to becomeinoperative due to the accelerational and centrifugal forces exerted onthe parts.

As nearly as can be determined, these defects in operation are caused bydeformation and disturbances of the elements from which the frame andhousing for the gearing and escapement mechanism is built up, and bydisplacement and distortion of the gearing and escapement elements inthe frame.

Difiiculty has also been encountered in providing a positive lock forthe setting mechanism which will unfailingly maintain the setting of thefuse in all conditions of use. Moreover, the usual types of tripmechanism for the firing pin place such a frictional load on the gearingthat the variations in such load impair the accuracy of control of thegearing by the escapement mechanism.

It is an object of the present invention to provide a novel mechanicaltime fuse which is reliable and accurate in operation while being safeto handle and easy to set for timed operation.

It is another object to provide such a device including a source ofpower adapted to deliver substantially uniform torque throughout theflight of the projectile, and multiplying gearing actuated thereby underthe control of an escapement mechanism.

It is another objectto provide such a device including a novelanti-friction type of trip for the firing pin.

It is a further object to provide such adevice including a rigid framecomprising an integral supporting member for the gearing and escapementmechanism It is another object to provide such a device in which thegearing is designed and arrangedto operate without interruption orinaccuracy regardless of variations in center distance of the gears dueto accelerational or-centrifugal forces;

It is another object to provide such adevice in whichthe firingmechanism is armed only by the discharge of the projectile andremainsarmed only during the flight thereof.

It is another object to provide such a device in which the timingmechanism may have a wide scope of adjustment with alarge-scale-facilitating rapid and accurate setting of thefuse.

Further objects and advantages will be ap-v parent from the followingdescription taken connection with the accompanying drawings inwhich:

Fig. 1 is a verticalsubstantially mid-sectional view of the nose of aprojectile in which a pre-. ferred form of the present invention hasbeen. incorporated; 4

Fig. 2 is a section taken substantially on the line 22' of Fig. 1,showing more particularly the construction of the source of power forthetiming mechanism;

Fig. 3 is a section taken substantially: on the lined-3 of Fig. 1,showing the multiplying gear ing-and escapement mechanism;

Fig. 4' is a perspective view of the-framememher which carries thereduction gearing and es.-v capement mechanism;

Fig. 5 is a section. taken substantially on the line 5-5 of Fig. 1,showing the trip mechansm; forthefiring pin: latch;

Fig. 6 is a perspective view, partly broken. away, of the frame memberwhich forms the mounting for the firing pin with its latch and tripmechanism Fig. 7 is a detail in side elevation of the, shell and nosecap, showing the setting scale;

Fig. 8 is a detail in. side elevation on a greatly enlarged scaleshowing portions of" a. meshing gear and pinion formed according to.the; con-- ventionalpractice in chronometric' devices;

Fig. 9 is a view similar to Fig. 8,: showing the positions assumed bythe gear and pinion when thecenter distance thereof is increased reasonof the effects of centrifugal force, eta;

Fig. 10 is a similar view of a. gear and; pin-ion formed in accordancewith, the teachingsof; the present invention; and I Fig. 11 is a viewsimilar to Fig. 10; showing the parts in the positions assumed when thevcenter distance thereof isincreas'ed as in, Fig. 9..

In. Fig. 1- of the drawings a: portion of ashell of.

conventional type is illustrated comprising a casing and a cap 2threaded thereon by means of a sleeve 3 of soft metal such as lead orcopper bonded to the casing and having threads engaging in internalthreads formed in the interior of the cap. The upper rim of the shell ispreferably provided with teeth 4, and the interior of the cap 2 isprovided with a corresponding annular series of teeth so arranged thatupon discharge of .the shell from its rifle, the threads of the softmetal member 3 are stripped, and an inwardly extending flange 6 thereofis clutched between the teeth 4 and 5 of the casing and caprespectively, thus securely locking the cap to the casing and preventingrelative rotation thereof.

A frame member I (Fig. 6) is mounted in the shell casing I in anysuitable manner as by means of a mounting plate 8 seated in acounterbore 9 in the top of the casing, keyed against rotation by meansof dowels H and maintained in its seat by means of a locking ring l2.The frame I is attached to the mounting plate 8 by suitable means suchas cap screws l3, and a partition plate I4 is rigidly connected to theframe as by means of cap screws l5.

A firing pin H3 is slidably mounted in the frame 1 and partition plateI4 in position to engage and detonate a cap ll of suitable explosivematerial mounted in the end of a cartridge l8 containing explosivematerial I9 for detonating the main charge of explosive contained in thebody of the shell. The firing pin is normally maintained retracted fromthe percussion cap II by means of a latch 2| pivoted at 22 in the framemember 'i and maintained by a spring 23 in engagement with a flange 24on the upper end of the firing pin. Means responsive to acceleration ofthe shell on discharge from the rifle for arming the firing pin isprovided in the form of a weight member 25 slidably mounted, in a recess25 in frame member I and bearing on a firing pin spring 21 which engagesthe firing pin. The firing pin spring 21 is normally released, but onmounting plate 53.

acceleration of the shell upon its discharge from a rifle, the weight 25is set back to the position illustrated in Fig. 1 in which the firingpin spring 27 is compressed. During the flight of the projectile, theset-back weight 25 is maintained in the position shown by the engagementof an inclined shoulder 28 on the frame I with the tapered upper portion29 of the weight member, this engagement being firmly maintained bycentrifugal force due to the rapid rotation of the shell.

Means are provided for tripping the latch 2| to allow the spring 21 toactuate the firing pin it a predetermined time interval after dischargeof the projectile. As here shown, this means comprises a sphericalweight member 3| seated in the periphery of a rotary carrier 32 which isslowly revolved during the flight of the projectile to roll the weightmember 3| into alignment with an opening 33 in a gate member 35 in theform of a cylindrical wall in the frame I. The opening 33 is adjacentthe upper end of the latch 2| whereby the weight member 3| can strikethe upper end of the latch by reason of centrifugal force operating onthe weight member, thus causing release of the latch.

As here illustrated, the carrier 32 is fixedly mounted on a shaft 34journalled in the supporting plate 8 and in a partition 35 formed in theframemember 1 below the gate wall 35. In order to provide greaterlatitude of adjustment than couldbe secured merely by the rotation ofthe spherical weight member 3| into registry with the opening 33 in thegate member 35, a cylindrical diaphragm 36 is freely J'ournalled on theshaft 34 within the gate member 35 and is provided with an opening 31similar to the opening 33. A pinion 3a is fixed to the shaft 34 andmeshes with a pinion 39 fixed as indicated at 4| in the partition 35 andmeshing with an internal gear 42 formed in the rim of the diaphragmmember 36. The sizes of the pinion 38, gear 39 and internal gear 42 areso proportioned that the diaphragm will make a suitable number ofrevolutions backward while the carrier 32 is making one revolutionforward. Thus, if the gear ratio is 4:1, the opening 31 in the diaphragmwill register with the opening 33 in the gate member at the same timethat the spherical weight member 3| is brought into registry therewithonce during four revolutions of the carrier. It i thus possible to setthe fuse so that the carrier will have to make up to slightly less thanfour revolutions before the tripping mechanism will be operated.

Means for rotating the carrier 32 at a predetermined speed during theflight of the projectile is provided in the form of a power source,multiplying gearing and an escapment mechanism. The power source hereillustrated is in the form of a spring 43 attached at one end to aweight member 44 freely journalled on a clamping bolt 45, and attachedat its other end to a main drive gear 46 as by means of a pin 41. Theweight member 44 is provided with a stud 48 arranged to traverse achannel 49 in a looking block 5| fixed as indicated at 52 to a cap Thechannel 49 is provided with an abutment 54 (Fig. 2) for the pin 48 and,adjacent the abutment 54, with an opening 55. The weight member isnormally urged upwardly with the pin 48 bearing in the bottom of thechannel 49 by suitable means such as a spring 56. In will be understoodthat the normal position of the weight 44 is with the pin 48 in thechannel 49 against the abutment 54. When discharge of the shell occurs,however, the rotation of the shell causes the weight 44 to be rotarilydisplaced, the pin 48 traversing the groove 45 until it strikes theopposite side of the abutment 54, whereupon the spring 56 expands andforces the pin 48 into the opening as illustrated in Fig. 1, whereby thespring 43 is wound up to store energy therein.

A pinion 51 meshing with the main drive gear 46 is fixedly mounted on ashaft 53 journalled in the mounting plate 53 and carrying on its lowerend a gear 59 fixed thereto as indicated at 6|. Gear 59 meshes with apinion 62 journalled on the exterior cylindrical surface of a clamp nut63 threaded on the bolt 45. A planet carrier disc 64 is formed on orrigidly connected with the pinion 62 and carries a plurality of studs 65on which are journalled planet gears 66 meshing on their outer edgeswith an internal gear 61 formed in the interior of the cap 2, and alsomeshing with a sun gear 58 having a splined connection 69 with the upperend of the shaft 34 for the tripping mechanism. It will thus be Seenthat if the cap 2 is held stationary, rotation of the gearing by thespring43 will cause rotation of the trip mechanism. On the other hand,if the main driving gear 46 is held stationary and the cap 2 rotated byhand, the trip mechanism may be set to any desired position.

In order to indicate the setting of the cap I and consequently of thetrip mechanism, a micrometer scale having a suitable zero line It (Fig.'7) is engraved on the shell casing I and as'eegsioa shown in Figs. 1'and 3, the planet carrier 64 is provided with peripheral gear teeth 12meshin with a pinion 13 mounted on a shaft 14 bearing at one end in themounting plate 53 and at the other end in a bearing plate 15 fixed asindicated at 16 to a gear frame member 11 (Fig. 4) rigidly connected asby means of cap screws [8 to the mounting plate 53.

A series of multiplying gearing is driven from .the pinion E3, themounting shafts of which bear at one end in the mounting plate 53 asindicated at 19, BI and 82 and at their other ends in bearing openings83, 84 and 85 formed in stepped surfaces 85, 81 and 88 of the gearinframe member l'l. An escapement wheel 89 driven by this multiplyinggearing is mounted'at one end as indicated at 91 in the mounting plate53 and at its other end in the opening 92 in the step 93 of the gearingframe. A pallet 94 is arranged to cooperate with the escapement wheel89, being mounted at 95 in the mounting plate 53 and at 96 in the step9'! of the gearing frame. A hair spring 98 for the pallet is providedhaving a suitable adjustin mechanism 99 mounted on the mounting plate53.

It will be understood that all the parts within the shell are subjectedto very heavy translational and rotational forces, and in particularcentrifugal forces generated by the extremely rapid rotation of theshell. It has heretofore been customary in devices of this charactertoemploy gearing of the type usually used in chronometric work in orderthat the usual formulas and operations might be adapted for use in thetiming mechanism for the shell. It has been found, however, as abovepointed out, that the stresses engendered particularly by centrifugalforces on the components of the gearing may be of such values as toimpair the accuracy of the gearing or even render it inoperative byreason of distortion of the frame and/or displacement and distortion ofthe gear shafts.

According to the present invention, it is proposed to substantiallyeliminate the possibility of distortion of the gear frame by forming thegear frame as an integral unit having steps or terraces for theaccommodation of the various steps of the gearing. Moreover, it is afurther feature of the invention to utilize a form of gearing in whichthe operation of the gearing is substantially unaffected by changes incenter distances thereof within reasonable limits, and the possibilityof the gearing being rendered inoperative by the causes above mentionedis substantially elminated. It has been found that the so-calledinvolute gearing in which the tooth contour may be said to be describedby a point on a line unwrapped from the base circle of the gear,possesses the desirable qualities above referred to. It is proposed,therefore, according to the present invention to incorporate involutegearing both as drive gearing for the trip mechanism and for theescapement mechanism for the purposes stated.

Figs. 8, 9, 10 and 11 illustrate the old and new types of chronometricgearing and the difference in operation brought about by the adoption ofthe involute type of gear tooth. Fig. 8 illustrates the ordinary form ofchronometric gearing in which the tooth contours are formed by simplearcuate lines joined by straight lines. As

there shown, thetooth engagement in, this form of gearing occurs mainlyatv and near the point of tangency of the pitch circles, and if thecenter distance of the gear and pinion is maintainedconstant so that thepitch circles are actually tangent, the gearing operates quitesatisfactorily. If the center distance is increased substantially,however, due to the accelerational or centrifugal forces encountered inthis art, a condition may occur such as illustrated in Fig. 9 in whichthe tooth contacts take place substantial distances from the pitchcircles which are no longer tan.- gent, and a wedging and lockingcondition may be encountered.

Fig 10 shows the typev of involute gearing which is incorporated in thechronometric gearing according to the present invention and which is soarranged that a constant gear ratio is-maintained betweenthe drivinggear and driven pinion irrespective of the point of engagement of. thegear teeth. When the center distance of a gear and pinion of this typeis increased, the operation' of the gearing isnot adversely affectedsince awed'ging condition is not encountered as will be seen by anexamination of Fig. 11. The only weight member 3! is defined by suitablere movable means such as'a pin Hll (Figs. 1 and 5) traversing the wallof the shell case and entering anotch I02 in the carrier 32. The pin andnotch are preferably so related that the weight member 3| is slightlyout of register with the openings 31 and- 33 in the diaphragm 36 andframe 1 respectively, the'distance out of registry corresponding to ashort time interval such as one tenth of a second. In this way it isimpossible for the trip to be inadvertently operated in any manner priorto the discharge of the shell. Moreover, the weight member 3! is thusretained in its pocket in the carrier 32 at all times prior to dischargeof the shell.

In. assembling the fuse mechanism, the supporting plate 8 with itsassociated parts including the frame 7, partition l4 and the partsmounted therein are inserted in the end of the shell case I, beingrigidly fixed therein by means of the keys H and locking ring l2 (Fig.1).

The power source and gearing assembly mounted on the plate 53 are theninserted in the cap 2, the bolt 45 being inserted loosely in the nut 63to hold the parts in the cap with freedom for rotation therein as aunit. The cap 2 is then threaded on the casing l, the splines 69 of theshaft 34 entering the splined hub of the sun gear 68. The cap .2 is thusthreaded down snugly on the casing l until the zero pointer N (Fig. 7)on the cap comes opposite the zero line 10 on the casing.

It will be understood that when the cap is being screwed onto thecasing, the timing member 32 is held stationary by the pin I01, thuspreventing rotation of sun gear 68. Since the drive gearing is'prevented from rotation in its frame by the engagement of the pin 48 ofthe weight member 44 against its abutment 54 in the groove 49, the

- operation.

to wedge the mounting plate 53 in the cap 2 on the inclined surfaces I03whereby the mounting plate 53 and all its associated parts are rigidlyconnected to the cap. The shell is now in condition for shipment andstorage preparatory to use.

When it is desired to use the shell, the pin IOI is Withdrawn and thecap 2 is unscrewed until the number on the scale H corresponding to theestimated range of the target comes opposite the zero line 10 on theproper ring of the micrometer scale on the shell. During the unscrewingof the cap 2, the timing member 32 and diaphragm 36 will be rotated awayfrom their zero positions a distance depending on the setting of the cap2, and it is the timed rotation of these parts back to their zeropositions under the control of the chronometric gearing which determinesthe time interval between discharge and detonation of the shell. Theshell is then inserted in the rifle and fired in the usual manner.

It may be desired to provide a temporary locking means for the cap withrespect to the shell after being set. This is readily accomplished byforming corrugations I04 (Fig. 7) on the periphery of the shell casinginto which corresponding corrugations I34 (Fig. 1) in the interior ofthe scale H may be caused to engage by a blow or pressure appliedthereto.

Upon discharge of the shell from the rifle, the longitudinalacceleration of the shell causes the cap 2 to strip the threads of thesoft metal sleeve 3, whereby the teeth 5 on the cap bite into the flange6 and force it against the teeth 4 on the shell casing, thus securelylocking the cap to the K shell. At the same time the set-back Weight 25is moved down to the position illustrated in Fig. l, compressing thefiring pin spring 27, the centrifugal force due to the rotation of theshell causing the set-back weight to move radially outward asillustrated whereby it is held in its lower position by the inclinedshoulder 28 of the frame member l.

Simultaneously with these functionings, the Weight member 44 is causedby its inertia to move down, compressing the spring 5B,'and at the sametime the cap 2 and associated parts move rotatively with respect to theweight member 44, causing the pin 43 to traverse the channel 49 until itstrikes the opposit side of the abutment 54. The spring 56 thereuponexpands and forces the pin 48 into the opening 55, thus holding theweight in its rotated position with respect to the cap 2, and causingthe main drive spring 43 to be held in its wound-up position. Torquefrom the spring 43 is thereupon transmitted through gear 46 pinion 5?,shaft 58, gear 59, pinion 62 and planet carrier 6 5 to the planets 65,causing planetation thereof.

When the shell is discharged, the cap 2 is tightly locked to the casingi, as above set forth, by the engagement of the teeth 4 and 5 in theflange 6 of deformable metal. The internal gear 61 in the cap 2 is thusmaintained stationary. Planetation of the planets 66, therefore, causesrotation of the sun gear 58, which rotation is transmitted through shaft34 to the carrier 32 to rotate the carrier back toward the zeroposition. This rotation of the Sun gear as is controlled by the geartrain driven from pinion 13 meshing with the gear 12 of the planetcarrier 64, the speed of which gear train is accurately governed by theescapement wheel 89 and pallet 94. After the time interval predeterminedby the setting of the cap 2 has elapsed, the carrier 32 and diaphragm 36will rotateback to their zero positions, at which time the openings 3'!and 33 lineup and permit the spherical weight member 3| to strike theupper end of the latch 2| as it is projected from the carrier 32 bycentrifugal force. The firing pin I6 is thus released to causedetonation of the shell in the usual manner.

If the flight of the shell should terminate for any reason prior to thedetonation thereof, as for instance, by a miscalculation of the settingin the fuse or for any other reason, as soon as the shell comes to rest,the firing pin spring 21 is permitted to expand since the set-backWeight 25 is no longer held in its armed position by centrifugal force,so that the shell is entirely safe to handle tional or centrifugalforces.

Although but one form of the invention has been shown and described indetail, it will be appreciated that variations in the precisearrangements shown are possible without departing from the spirit of theinvention as defined in the claims appended hereto.

What is claimed is:

1. In a mechanical time fuse for explosive projectiles, a source ofpower, involute gearing driven thereby, a firing pin movably mounted inthe fuse, a latch movably mounted in the fuse normally positioned toengage and hold the firing pin inoperative, releasing means thereforcontrolled by said gearing, and an escapement mechanism governing saidgearing, said release means comprising a roll member moveable bycentrifugal force to engage and trip th latch, a gate member having anaperture, means for positioning the aperture in registry with the latch,and means actuated by said gearing to roll said roll member on th gatemember into registry with saidaperture so that the roll may traverse theaperture and engage and trip the latch.

2. A mechanical time fuse as set forth in claim 1 including further aframe for uniting the elements of said gearing, said frame comprising aplurality of circular plate members providing bearings for the gearing,including an integral intermediate frame member having surfaces in aplurality of planes providing bearings for a plurality of gears arrangedin stepped planes, and clamping means traversing the plate members forattaching the end plates to the intermediate frame member.

WILLIAM L. McGRATI-I. MAURICE P. WHITNEY.

